High molecular weight sodium hyaluronate

ABSTRACT

A novel mutant microorganism Streptococcus zooepidemicus HA-116 ATCC 39920, has been produced. The microorganism produces large amounts of high molecular weight hyaluronic acid. The invention provides a method of obtaining such microorganisms. 
     The invention also concerns a method of obtaining sodium hyaluronate which comprises growing with vigorous agitation a microorganism of the genus Streptococcus under appropriate conditions in a suitable nutrient medium containing a sugar component as a carbon source. The sugar component is present in a substantially constant concentration between 0.2 and 10 grams per liter. The medium has a substantially constant pH between about 6.0 and 7.5 and includes a substantially constant magnesium ion concentration above 0.05 grams per liter. The sodium hyaluronate excreted into the medium by the organism is purified using methods involving precipitation, redissolving and reprecipitating the hyaluronate. Composition of sodium hyaluronate which are characterized by an absence of pyrogenicity and skin irritation are obtained.

BACKGROUND OF THE INVENTION

This invention concerns a process for the production of the sodium salt of high molecular weight hyaluronic acid by large-scale fermentation of a microorganism of the genus Streptococcus.

Hyaluronic acid is a naturally occurring glycosaminoglycan consisting of a linear polymer of molecular weight of 50,000-13,000,000 daltons. It is a polysaccharide made of a repeating units of glucuronic acid and N-acetyl-glucosamine, bound by alternating β1-3 and β1-4 bonds.

Hyaluronic acid is present in various connective tissues of animals, such as skin and cartilage. Some organs are specifically rich in hyaluronic acid, such as the umbilical cord, synovial fluid, the vitreous humor and rooster combs. In addition, hyaluronic acid is produced by various microorganisms, such as streptococci Type A and C.

In skin and cartilage, the role of hyaluronic acid is to bind water and retain the tonicity and elasticity of the tissue. In joint fluids, the viscous hyaluronic acid solution serves as a lubricant to provide a protective environment to the cells. A solution of ultrapure hyaluronic acid from rooster combs has been in use for several years as a supportive medium in opthalmic surgery, see U.S. Pat. No. 4, 141,973 of E. A. Balazs (1979). A similar preparation has been shown to be beneficial in the treatment of inflamed knee joints of race horses. Another use of hyaluronic acid results from its highly hydrophilic nature, making it an ideal constitutent of moisturization lotions for cosmetic use, U.S. Pat. No. 4, 303,676 of E. Balazs (1981).

Hyaluronic acid has been isolated from the various biological sources, as described above, including microbial broth. The isolation and characterization of hyaluronic acid has been described by Meyer et al., J. Biol. Chem. 107,629 (1934); J. Biol. Chem. 114,689 (1936), and has recently been reviewed in Methods in Enzymol. 28, 73 (1972). The structure of hyaluronic acid was elucidated by Weissman et al., J. Am. Chem. Soc. 76, 1753 (1954) and Meyer, Fed. Proc. 17, 1075 (1958).

The production of hyaluronic acid by Streptococcus was first shown by Forrest et al., J. Biol. Chem. 118, 61 (1937), and further elaborated on since by various researchers, such as Roseman et al., J. Biol. Chem 203,213 (1953), Pierce and White, Proc. Soc. Exp. Biol. Med. 87, 50 (1954), U.S. Pat. No. 2,975,104 of G. H. Warren (1961), and Sunghara et al., J. Biol. Chem. 254, 6252 (1979), demonstrating the identity of hyaluronic acid from animal and microbial sources. Procedures have been published for batch fermentations of Type A streptococci and hyaluronic acid isolation on small to medium scales Thonard et al., J. Biol. Chem. 239, 726 (1964); Holmstrom and Ricica, Appl. Microbio. 15, 1409 (1967); Kjems and Lebech, Acta Path. Microbiol. Scand. 84, 162 (1976). These procedures included anaerobic fermentations of the pathogenic bacteria, and resulted in yields of 0.4-1 grams/liter of hyaluronic acid of a molecular weight of 700,000 or less.

Other procedures have concerned the aerobic fermentation of streptococci to produce hyaluronic acid such as Japanese Pat. Publication Kokai No. 58-056692, published Apr. 4, 1983, by inventors, Akasaka H, et al. Other publications such as, U.S. Pat. No. 4,141,973, Feb. 27, 1979 by E. A. Balazs, concerned the production and purification of hyaluronic acid from sources such as animal connective tissue. The hyaluronic acid production and purification procedures disclosed in the prior art did not, however, yield hyaluronic acid of an average molecular weight of greater than 2.0×10⁶ daltons. This is largely due to the fact that hyaluronic acid is easily degraded by shearing or oxidized in reactions catalyzed by impurities or metal ions present in the hyaluronic acid composition.

The novel process described herein results in hyaluronic acid of a molecular weight from about 1×10⁶ to about 4.0×10⁶ daltons, in a yield of about 2 grams/liter in anaerobic fermentation and about 4-6 grams/liter in aerobic fermentation. This was made possible by producing a mutant strain of a Type C Streptococcus zooepidemicus, HA-116, ATCC 39920, which is a high producer of hyaluronic acid and is haemolysin minus, i.e. of negligible pathogenicity. Aerobic Fermentation of S. zooepidemicus, HA-116, ATCC 39920 and subsequent purification of hyaluronate have resulted in batches of sodium hyaluronate with an average molecular weight of greater than 3.5×10⁶ daltons. This invention is the first method of producing and purifying such high molecular weight soidum hyaluronate by bacterial fermentation.

The first stage of the isolation procedure results in hyaluronic acid that is non-pyrogenic and non-irritating. This material can be further purified according to the methods of this invention to produce ultrapure, non-inflammatory hyaluronic acid suitable for clinical use.

SUMMARY OF THE INVENTION

The invention concerns a microorganism of the species Streptococcus zooepidemicus, HA-116, ATCC 39920, and mutants derived therefrom which are capable of producing sodium hyaluronate by fermentation and excreting it into the surrounding medium.

The invention also concerns a method of obtaining sodium hyaluronate which comprises growing with vigorous agitation a microorganism of the genus Streptococcus under appropriate conditions in a suitable nutrient medium. The medium includes a sugar component as the carbon source in a substantially constant concentration between about 0.2 and 10 grams per liter, has a substantially constant pH between about 6.5 and 7.5 and also includes a substantially constant magnesium ion concentration above 0.05 gram per liter. The microorganism produces sodium hyaluronate and excretes it into the medium. The sodium hyaluronate is then recovered from the medium.

The sodium hyaluronate is recovered from the medium by a method comprising treating the medium containing the microorganism so as to remove the microorganism and other materials insoluble in the medium, precipitating the sodium hyaluronate from the medium, e.g. precipitation with organic solvents, and recovering the precipitate. The precipitate can then be ground and dried. Compositions of sodium hyaluronate characterized by an absence of pyrogenicity and inflammatory activity can be produced by these methods.

The present invention also concerns a method for selecting microorganisms which produce enhanced amounts of hyaluronic acid and which lack hemolytic activity. The method comprises treating microorganisms that produce hyaluronic acid with a suitable mutagen to produce mutants thereof, and growing the mutants on a suitable solid medium. The mucoid colonies are identified, and recovered. The recovered colonies are grown on blood agar and colonies which to not lyse hemoglobin are selected.

DETAILED DESCRIPTION OF THE INVENTION

The present invention concerns a method of obtaining high molecular weight sodium hyaluronate from microorganisms of the genus Streptococcus, e.g. S. zooepidemicus or S. equisimilis. The method comprises growing microorganisms of the genus Streptococcus with vigorous agitation under appropriate conditions and in a suitable nutrient medium. The medium includes a sugar component as the carbon source in a substantially constant concentration between about 0.2 and 10 grams per liter, a substantially constant magnesium ion concentration above about 0.05 grams per liter and a substantially constant pH between about 6.5 and 7.5. The microorganisms produce sodium hyaluronate and excrete it into the medium. The sodium hyaluronate is then recovered from the medium.

Any hyaluronic acid producing species of Streptococcus can be used in practicing this invention, e.g. S. zooepidemicus, S. equisimilis or S. pyogenes. The preferred species is S. zooepidemicus and the strain is S. zooepidemicus HA-116 ATCC 39920 which is a mutant strain produced according to a method of this invention for obtaining microorganisms which produce an enhanced amount of hyaluronic acid.

The sodium hyaluronate can be obtained by growing the Streptococcus under aerobic or anaerobic conditions. In a preferred embodiment of the invention the appropriate growing conditions comprise aeration of the medium at a rate greater than about 0.5 volumes of air per volume of medium per minute (vvm). An aeration rate of 1-2 vvm is generally used, however greater aeration rates may be desirable. In this preferred embodiment the suitable nutrient medium comprises per liter, casein hydrolysate about 10 to 30 grams, yeast extract about 5 to 15 grams, NaCl about 2 grams, MgSO₄.7H₂ O above about 0.5 grams, K₂ HPO₄ about 2.5 grams, and glucose about 2 to 10 grams.

The sodium hyaluronate can be recovered by treating the medium containing the microorganism so as to remove the microorganism and other materials insoluble in the medium, e.g. by filtration or centrifugation. The sodium hyaluronate is then precipitated from the medium and recovered. The precipitate can then be ground to uniform size particles and dried.

In one embodiment of the invention the sodium hyaluronate is recovered by adjusting the pH of the medium containing the microorganism to a pH of about 5.0 and then heating the medium for a suitable period of time at a temperature between about 80° and 95° C., e.g. heating for 20 minutes at a temperature of about 90° C. After heating the microorganism and other insoluble materials are removed. The preferred method of removal is by filtration with a filter aid such as diatomaceous earth.

The sodium hyaluronate can be precipitated from the medium or filtrate by adding a first organic solvent, such as isopropanol, to the medium. The precipitate is redissolved in 3% aqueous sodium acetate and then reprecipitated with a second organic solvent such as ethanol. The second precipitate is redissolved in 3% aqueous sodium acetate and activated charcoal is added to form a suspension. The suspension is filtered and a third organic solvent e.g. acetone is added to produce a precipitate of sodium hyaluronate. The first, second and third organic solvents can each be isopropanol, ethanol or acetone. Alternatively the hyaluronate can be precipated by the same organic solvent in each step, e.g. sodium hyaluronate is precipitated from the medium by using isopropanol in all three of the precipitation steps.

In another embodiment of the invention the pH of the medium containing the microorganism is adjusted to about 7.0 and the medium is cooled to a temperature between about 4° and 15° C. prior to treating the medium to remove the microorganism. The medium is then diluted with 3% aqueous sodium acetate to the extent necessary to permit subsequent treatment e.g. three to four-fold.

In a preferred embodiment of the invention, the sodium hyaluronate precipitate is redissolved in 0.15M aqueous NaCl and cetyl-pyridinium chloride is added to form the cetyl-pyridinium salt of hyaluronic acid. The cetyl-pyridinium salt is dissolved in aqueous NaCl, e.g. at least 1M NaCl and sodium hyaluronate is recovered therefrom by addition of organic solvent e.g. ethanol precipitating the sodium hyaluronate.

This sodium hyaluronate precipitate can be redissolved in 0.15M aqueous NaCl. Cetyl-pyridinium chloride is added to again form the cetyl-pyridinum salt of hyaluronic acid. The hyaluronic acid salt is dissolved in NaCl (at least about 1M) and the resulting solution is contacted with a magnesium silicate absorbant, e.g. Florisil™ to remove impurities and residual cetyl-pyridinium ions. The solution is then sterilized and sodium hyaluronate is precipitated by the addition of sterile organic solvent, e.g. sterile isopropanol. The sodium hyaluronate so produced can be air dried under sterile conditions and is suitable for use in compositions of cosmetic grade and clinical grade sodium hyaluronate and other suitable carriers, e.g. glycerol, polypropylene glycol, sorbitol, collagen, polyethylene glycol.

The cosmetic grade composition of sodium hyaluronate produced by the methods of this invention is characterized by an absence of skin irritation. It contains between about 87% and 91% sodium hyaluronate of a molecular weight between about 700,000 and 1,500,000 daltons and a ratio of glucoronic acid to N-acetyl glucosamine of 1:1, from about 8% to about 12% by weight water, from about 4% to about 5% by weight sodium ion, less than about 0.1% by weight protein, less than about 0.05% by weight sulfate, and less than about 0.5% by weight nucleic acid.

The clinical grade composition of sodium hyaluronate of this invention is characterized by an absence of pyrogenicity and inflammatory activity. It contains between about 88% and 92% by weight sodium hyaluronate of an average molecular weight from about 2 to about 3.5×10⁶ daltons and a glucuronic acid to N-acetyl glucosamine ratio of 1:1, from about 8% to about 12% by weight water, from about 4% to about 6% by weight sodium ion, less than 0.01% by weight protein, less than 0.001% by weight sulfate, less than 0.02% by weight nucleic acid and less than 0.2% by weight neutral sugar.

A preferred ultrapure composition of sodium hyaluronate produced by the methods of this invention is characterized by a minimum limiting viscosity of about 3.5 m³ /kg, a minimum average molecular weight of about 3.5×10⁶ daltons, a specific optical rotation measured at 25° C. and at a wavelength of 436 nm from about 155° to 165°, a protein content of less than about 1 mg/gram, an absorbance at the wavelength of 257 nm of less than about 0.5, endotoxin of less than about 0.05 ng/ml., less than about 0.2 mg/g of iron, less than about 0.2 mg/g of copper, and an infiltration of less than about 200 white blood cells per mm³ of aqueous humor of owl monkey eye when 1 ml of a 1% solution of the composition dissolved in physiological buffer is implanted in the vitreous replacing about one-half the existing liquid vitreous.

Compositions of high molecular weight sodium hyaluronate of a average molecular weight greater than 3.5×10⁶ daltons and of different grades of purity have also been produced by the methods of this invention.

The vitreous test in the Owl Monkey Eye was performed essentially as described in U.S. Pat. No. 4,141,973 of E. A. Balazs (1979).

The invention also concerns the microorganism Streptococcus zooepidemicus HA-116 ATCC No. 39920 or mutants derived therefrom. This microorganism was derived by a method of selecting microorganisms which produce an enhanced amount of hyaluronic acid and which lack hemolytic activity. The method comprises treating microorganisms that produce hyaluronic acid, such as microorganisms of the genus Streptococcus, with a suitable mutagen capable of producing mutants of the organism, e.g. nitrosoguanidine. The mutants are grown on a suitable solid medium, e.g. Todd-Hewit agar, and mucoid colonies are identified. These colonies are recovered from the solid medium and grown on blood agar. The colonies which do not lyse hemoglobin are then selected and used for the production of hyaluronic acid in accordance with the methods of this invention.

EXPERIMENTAL DETAILS Bacteria Selection and Mutation Nitrosoguanidine Mutagenesis

Bacteria of the genus Streptococcus were treated for 40 min with 100 mg/ml of N-methyl-N'-nitro-N nitrosoguanidine in Tris-maleic buffer, pH 6.0, and then allowed to segregate on Todd-Hewitt agar plates for selection of high producers or on blood agar plates for Hemolysin minus selection. The survival rate of the bacteria was usually about 0.1%. Various Type C Streptococci obtained from hospital collections were treated as described above.

Selection for High Production

Visual evaluation of the clones was used for selection of large mucoid colonies. One such colony was obtained from an isolate of a strain which has been typed by the National Streptococcal Reference Center, of the Israeli Ministry of Health, as a variant of Type C Streptococcus equisimilis (designated as HA-100). Subsequent tests based on "API 20 Strep" tests (API SYSTEM, S.A. FRANCE) for identification of Streptococci strains, indicate that HA-100 is more closely related to S. zooepidmicus.

Selection for Hemolysin Minus Mutants

Strain HA-100 was subjected to the mutagenis procedure described above and hemolysin minus [hem. (-)] colonies were examined both for hemolysin activity and for hyaluronic acid production in test-tube fermentation. One hem.(-) mutant which was also a high producer of hyaluronic acid was chosen and used for large scale hyaluronic acid production. This mutant was designated HA-116. "API 20 Strep." tests indicate that HA-116 is a strain of S. zooepidemicus. Streptococcus zooepdimicus HA-116 has been deposited with the American Type Culture Collection, 12301 Parklawn Drive, Rockville, Md 20852, pursuant to the provisions of the Budapest Treaty on the International Recognition of the Deposit of Microorganisms for the Purpose of Patent Procedure, and has been assigned accession number ATCC 39920.

THE FERMENTATION PROCESS

In addition to the use of the selected mutant HA-116, we have devised several other unique procedures to increase the yields and the molecular weight of the hyaluronic acid produced by bacterial fermentation and to shorten fermentation time. This includes (i) maintenance of high levels of magnesium ion concentrations; and (ii) performance of aerobic fermentations with a high rate of aeration and vigorous agitation.

In a preferred embodiment of the invention the composition of the fermentation medium is as follows:

    ______________________________________                                         Component      Concentration (grams/liter)                                     ______________________________________                                         Casein hydrolysate                                                                            20                                                              Yeast extract  10                                                              NaCl           2                                                               MgSO.sub.4.7H.sub.2 O                                                                         1.5                                                             K.sub.2 HPO.sub.4                                                                             2.5                                                             Glucose        5                                                               ______________________________________                                    

The pH of the medium is maintained at about 7.0 by continuous addition of 5N NaOH upon demand of a pH controller. Concomitant addition of an identical volume of 50% (w/v) glucose is performed by a pump connected in parallel to the controller.

The cultivation of the bacteria can be conducted with or without aeration. In both cases the cultivation is preferably conducted with vigorous agitation. The aeration is preferably at a rate of about 1-2 volume of air per volume of medium per minute. Yields in the non-aerated fermentors are from about 2 to about 3 g/l of hyaluronic acid with an average M.W from about 1.5 to about 2×10⁶. Fermentation with aeration yields from about 4 to about 6 g/l of hyaluronic acid with an average M.W of from about 2.2 to about 3.3×10⁶ daltons. The average M.W. is determined based on viscosity measurements known to those of ordinary skill in the art. In both cases, the incubation time is around 12 hours when a 5% (v/v) inoculum of bacteria which has been grown to 2.0-2.5 O.D. units measured at 660 nm is used. At the end of the fermentation, the density of the biomass is equivalent to a turbidity of 8-13 O.D. units.

ISOLATION AND PURIFICATION OF HYALURONIC ACID

The purification procedure can be divided into two stages, the first one leading towards a "cosmetic grade" sodium hyaluronate, while the second stage is a further purification of the cosmetic grade towards a high purity, non-inflammatory material suitable for clinical application.

Stage I

This stage comprises the removal of the bacteria and other insoluble materials by filtration, followed by three successive sedimentations by isopropanol and treatment with activated charcoal.

When only cosmetic grade material is prepared, the fermentation broth is heated for 20 minutes at a temperature of about 90° C. and at a pH of about 5.0 prior to filtration. At this time no dilution is necessary. For the preparation of a clinical-grade high molecular weight material, the fermentation broth is cooled with ice to a temperature from about 10° to about 15° C., diluted 3- to 4-fold with 3% sodium acetate, adjusted to a pH of about 7.0 and then subjected to filtration. Diatomaceous-earth type filter-aid, e.g. 0.5 grams/liter of Celatom FW-14™, Eagle-Picker Industries, Inc., Cincinnati, Ohio, is used in conjunction with a vacuum-type or pressure filter. Sodium hyaluronate is precipitated from the filtrate by addition of 1 volume of isopropanol. The precipitate is redissolved in an equal volume of 3% sodium acetate, and the material precipitated again with isopropanol. The second precipitate is redissolved in 3% sodium acetate, then 1 gram/liter of activated charcoal is added and the mixture is stirred for about 1 hour. This suspension is filtered and the sodium hyaluronate is precipitated by addition of isopropanol, washed with isopropanol and finally ground and air-dried to give a "cosmetic-grade" product.

Stage II

Cosmetic-grade sodium hayluronate is purified by two successive precipitations of its cetyl-pyridinium salt, followed by adsorption of impurities on a magnesium silicate, e.g. Florisil™ column.

Cetyl-Pyridinium Chloride (CPC) Precipitation: Cosmetic grade material from Stage I is dissolved in 0.15M NaCl to give a hyaluronate solution of a concentration of about 0.25 percent. One volume of 10% CPC in 0.15M NaCl is added to about 8 volumes of the 0.25% hyaluronate solution. The cetyl-pyridinium salt is separated by decantation and centrifugation, washed with 0.15M NaCl and then redissolved in 2M NaCl containing 15% ethanol, to give a solution of about 0.2% hyaluronate. Hyaluronic acid is sedimented as the sodium salt by addition of 1 volume of isopropanol. The pellet is washed with isopropanol and redissolved in 0.15M NaCl for a repeated CPC precipitation and then redissolved in 1M NaCl for Florisil™ treatment.

Florisil™ Adsorption: A solution of about 0.25% sodium hyaluronate in pyrogen-free 1M NaCl is passed through a column of 30-60 mesh activated Florisil™ e.g. 200 gr Florisil™ per 10 liter of solution. The solution is then rendered germ-free by filtration through a 0.2 μm filter. Sodium hyaluronate is precipitated by filtersterilized isopropanol (1 volume), followed by washing with sterile analytical grade ethanol. The precipitate is finally dried by a stream of sterile air.

The yield of hyaluronic acid in this procedure is about 60-70%.

PROPERTIES OF THE PRODUCT SODIUM HYALURONATE Sodium Hyaluronate Grade I

Sodium hyaluronate grade I is "cosmetic grade" sodium hyaluronate that is obtained after purification stage I. Its properties are as described below:

a. Content of Sodium Hyaluronate: 87-91%, assayed by the modified carbazole method, Bitter and Muir, Anal. Biochem. 4, 330 (1962) using Sigma hyaluronic acid Type I, cat. #H 1751, as a reference standard.

b. Average Molecular Weight: From about 700,000 to about 1,500,000 daltons, calculated from the limiting viscosity number esentially as described by Laurent et al., Biochem. Biophys. Acta 42, 476 (1960). A representative calculation of intrinsic viscosity and molecular weight is shown below.

Intrinsic Viscosity and Molecular Weight: The viscosity of sodium hyaluronate (NaHA) solutions was measured with a capillary viscometer. The flow time (t) of the sample was measured and compared with the flow time (t) of pure solvent.

Viscometer: Cannon-Ubbelohde dilution viscometer size 100 (Cannon Instrument Co.).

Solution: 0.1% sodium hyaluronate in 0.2 M sodium chloride

Temperature: 25° C.±0.01

Calculation of intrinsic viscosity:

    ______________________________________                                         ηrel. -                                                                             Relative viscosity expresses the change in                                     solution viscosity relative to the pure solvent.                       ηrel. -                                                                             ##STR1##                                                             ρ    density                                                               t -      flow time in seconds                                                  ηsp -                                                                               Specific voscosity. Measures the increase                                      in viscosity over unity.                                               ηsp -                                                                               ##STR2##                                                             ηsp/C -                                                                             reduced viscosity                                                     C -      concentration in gr/ml                                                (η) -                                                                               intrinsic viscosity (limiting viscosity number)                                 ##STR3##                                                             ______________________________________                                    

Determination of intrinsic viscosity (η):

The viscosity of a 0.1% sodium hyaluronate solution and of two fold, three fold and four fold dilutions of this solution were measured. The concentration of sodium hyaluronate was determined by the carbozole method. ηsp/C was plotted versus C and extrapolated linearly to C=0. (η) was obtained from the intersect of the line with the Y-axis.

Determination of molecular weight:

The molecular weight of sodium hyaluronate was calculated from the empirically-established Mark-Houwink relationship.

    (η)=0.0403·M.sup.0.775

The above relationship was used to determine the molecular weight of various lots of NaHA produced. The relationship is shown in Table I.

                  TABLE I                                                          ______________________________________                                         [η], ml/g                                                                              Mol. Wt., Dalton                                                   ______________________________________                                           800         350,000                                                          1,200         590,000                                                          1,600         860,000                                                          2,000       1,145,000                                                          2,600       1,600,000                                                          3,200       2,100,000                                                          ______________________________________                                    

c. Ratio of Glucuronic Acid/N-Acetyl Glucosamine (NAG): 1/1; NAG assayed by the modified method of Morgan and Elson, methods in Carbohydrate Chemistry 8, 89 (1980).

d. WATER CONTENT: 10%±2%.

e. Protein: Less than 0.1%, assayed by the Coomasie blue method of Bradford, Anal. Biochem. 72, 248 (1976).

f. Sodium Ions: 5%±1%, assayed by flame photometry.

g. Sulfate Content: Less than 0.05%, as determined after hydrolysis in hydrochloric acid by the turbidometric method of Roden et al., Methods Enzymol. 28, 73 (1972).

h. Nucleic Acids: Less than 0.5%, assayed by measurement of the absorbance of light through a 1% solution at a wavelength of 260 m.

i. Absence of Skin Irritation: This is determined for a 1% solution by (i) Draize dermal irritation test in rabbits, Draize, J. H., in: "Appraisal of the Safety of Chemicals in Food, Drugs and Cosmetics". Association of Food and Drug Officials of the United States, Austin, Tex., pp. 46-49 (1959); (ii) Delayed contact hypersensitivity test in Guinea pigs, Magnusson and Kligman, J. Invest. Dermatol. 52, 268 (1969).

Sodium Hyaluronate Grade II

Sodium hyaluronate Grade II is "clinical grade" sodium hyaluronate obtained after purification stage II. Its properties are as described below:

a. Content of Sodium Hyaluronate: 88-92%.

b. Average Molecular Weight: More than 7×10⁵ daltons, usually in the range from about 2 to about 3.5×10⁶ daltons, calculated from the limiting viscosity number as described above.

c. Ratio of Glucuronic Acid/N-acetyl Glucosamine: l/l.

d. Water Content: 10%±2%

e. Protein: Undetectable (less than 0.01%).

f. Sodium Ions: 5%±1%

g. Sulfate Content: Undetectable (less than 0.001%).

h. Nucleic Acids: Undetectable (less than 0.02%).

i. Neutral Sugars: Undetectable (less than 0.2%). The neutral sugars are determined in samples after hydrolysis. Hydrolysis is for 1 hour at 120° C. in 2N trifluoroacetic acid followed by vacuum drying. Thin layer chromatography is preformed on silicagel thin layer plates (0.2 mm), pretreated with 0.02 M sodium acetate. Sample hydrolysates are loaded along with reference standards and run in acetone: water, 90:10. The sugar spots are detected by charring with sulfuric acid.

j. Pyrogenicity: Negative. Pyrogenicity is measured by the standard methods known to those of ordinary skill in the art, after injection of a 1% solution in rabbits.

k. Absence of Inflammatory Activity: This property is determined by an sensitive assay method utilizing mice. The method is based on the migration of white blood cells, mainly polymorphonuclear cells and macrophages, into the peritoneum after introduction of an inflammatory agent. These cells are sensitized by the inflammatory process to produce superoxide radicals. The migration and sensitization are assayed by the following procedure: 1 ml samples are injected intraperitoneally, into groups of 2 to 3 mice. 24 hours later the peritoneum of each animal is washed 3 times with 5 ml of Earle's medium. The washes from the mice in each group are combined. Cells are sedimented at 1,500 RPM for 10 min, and resuspended in 1 ml for counting. The volumes of the samples are then adjusted to give 4×10⁶ cells/ml, and 0.25 ml portions are taken for 90 min incubation with 0.5 ml of 2 mg/ml cytochrome C and graded amounts (0, 2, 10, and 20 mg final) of phorbol myristate acetate (PMA). PMA is an activator of the oxidative "burst" system. The media are centrifuged at 1,500 RPM for 15 min and the absorbance of the supernatants is determined at 550 nm.

Inflammation is indicated by an increase in both the number of peritoneal cells and the maximal ability to respond to PMA and reduce the cytochrome C. Hence, an index of inflammation is defined as the activity (in nmoles of superoxide radicals formed) of all the white cells obtained from one mouse. A sample is regarded as non-inflammatory if the inflammation index is not significantly higher than that obtained from mice injected with saline alone. 

What is claimed is:
 1. A composition characterized by an absence of pyrogenicity and inflammatory activity and by the absence of proteins of animal origin which comprises between about 88% to 92% by weight sodium hyaluronate and from about 8% to 12% by weight water, the sodium hyaluronate being characterized by a minimum viscosity of about 3.5 m³ /Kg, an average molecular weight from about 3.5×10⁶ daltons to about 4.0×10⁶ daltons, a glucoronic acid to N-acetyl glucosamine ratio of 1:1, from about 4% to about 6% sodium ion, a specific optical rotation measured at 25° C. and at a wavelength of 436 nm from about 155° to 165°, less than 0.01% by weight protein, less than 0.001% by weight sulfate, less than 0.02% by weight neutral sugar, less than 0.05 ng/ml of endotoxin, less than 0.2 mg/g of iron and less than 0.2 mg/g of copper. 